Resonance Energy Transfer in a Genetically Engineered Polypeptide Results in Unanticipated Fluorescence Intensity

The fluorescence intensity of a C-terminal acceptor chromophore, N-(7-dimethylamino-4-methyl coumarin (DACM), increased proportionally with 280 nm irradiation of an increasing number of donor tryptophan residues located on a β-sheet forming polypeptide. The fluorescence intensity of the acceptor chromophore increased even as the length of the β-sheet edge approached 256 Å, well beyond the Förster radius for the tryptophan–acceptor chromophore pair. The folding of the peptides under investigation was verified by circular dichroism (CD) and deep UV resonance Raman experiments. Control experiments showed that the enhancement of DACM fluorescence occurred concomitantly with peptide folding. In other control experiments, the DACM fluorescence intensity of the solutions of tryptophan and DACM did not show any enhancement of DACM fluorescence with increasing tryptophan concentrations. Formation of fibrillar aggregates of the substrate peptides prepared for the fluorescence studies was undetectable by thioflavin T (ThT) fluorescence.     

Janus Gold Nanostars–Mesoporous Silica Nanoparticles for NIR-Light-Triggered Drug Delivery

Janus gold nanostar–mesoporous silica nanoparticle ( AuNSt–MSNP ) nanodevices able to release an entrapped payload upon irradiation with near infrared (NIR) light were prepared and characterized. The AuNSt surface was functionalized with a thiolated photolabile molecule ( 5 ), whereas the mesoporous silica face was loaded with a model drug (doxorubicin) and capped with proton-responsive benzimidazole-β-cyclodextrin supramolecular gatekeepers ( N 1 ). Upon irradiation with NIR-light, the photolabile compound 5 photodissociated, resulting in the formation of succinic acid, which induced the opening of the gatekeeper and cargo delivery. In the overall mechanism, the gold surface acts as a photochemical transducer capable of transforming the NIR-light input into a chemical messenger (succinic acid) that opens the supramolecular nanovalve. The prepared hybrid nanoparticles were non-cytotoxic to HeLa cells, until they were irradiated with a NIR laser, which led to intracellular doxorubicin release and hyperthermia. This induced a remarkable reduction in HeLa cells viability.     

Janus-type isopropyl groups revealed by 1H-NMR spectra of alkylpyridines with lanthanide shift reagents (LSR)

Two Isomeric pyridines were designed and prepared : 2-isopropyl-4,5,6-trimethyl-(3) and 2-isopropyl-3,4,6-trimethyl-pyridine (7); the latter, with a buttressed isopropyl, leads to much lower induced shifts by Eu(dpm)₃ and Pr(dpm)₃ than the former, owing to the conformation in which the Janus-type iPr group how to the LSR a t-butyl-like face.     

The standard enthalpies of formation of some dibenzoannelated cycloalkanols

The heats of combustion of trans-9,10-bis-hydroxymethyl-9,10-dihydrophenanthrene, trans-5-hydroxymethyl-5,6-dihydro-7H-dibenzo[a,c]cyclohepten-6-ol, 5-hydroxymethyl-5,6-dihydro-7H-di-benzo[a,c]cycloheptene, 6-hydroxymethyl-5,6-dihydro-7H-dibenzo[a,c]cycloheptene, 5H-dibenzo-[a,d]cyclohepten-5-ol and 5H-10,11-dihydrodibenzo[a,d]cyclohepten-5-ol were measured by means of a Gallenkamp adiabatic bomb calorimeter. Uncertainties in the determination of the heats of combustion ranged between 0.2 and 0.3%. The enthalpies of formation and atomization for the six compounds were derived. The experimental values of the heats of atomization were compared with those calculated using the Allen–Skinner bond energy scheme. Conclusions about energetic contributions which stabilize the structure of the investigated compounds were drawn.     

Dynamic light scattering and cryogenic transmission electron microscopy investigations on metallo-supramolecular aqueous micelles: evidence of secondary aggregation

Metallo-supramolecular diblock copolymers consisting of a polystyrene (PS) block connected to a poly(ethylene oxide) (PEO) block by a bis(terpyridine)ruthenium complex (PS₂₀-[Ru]-PEO _y ) were used to prepare aqueous micelles. The length of the PS block was kept constant, while two PEOs of different molecular weight were used. The resulting hydrated micelles and aggregates were characterized by a combination of cryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering measurements. The results were compared to those obtained for a covalent counterpart (PS₂₂-b-PEO₇₀). Cryogenic transmission electron microscopy allowed visualization of the PS core of the micelles. Moreover, the aggregates result from clustering of individual micelles.     

Evaluation of transversal and longitudinal dispersion in a flow injection system by exploiting laser induced fluorescence: influence of flow-cell positioning

A fully mechanized set-up was built for the experimental determination of bi-dimensional dispersion with high spatial resolution (2400 μm²). Gravitational and wall effects in a single stream were evaluated by using time-based sampling and a micro-flow cell. Vertical upward and downward flows as well as horizontal flows were investigated. Ethylene glycol (MEG) and Rhodamine B in MEG were used as carrier and sample solutions, respectively. Longitudinal profiles were obtained by laser induced total fluorescence (LIF) at up to 19 transversal sites and combined to generate high-resolution bi-dimensional profiles. A two frontal maxima pattern was observed for all flows. The volumetric fraction of RB shape was highly stretched for downward flow and there was high asymmetry for horizontal flow. The sensitivity of three dispersion parameters was evaluated: maximum peak value, peak half-width at half-height, and peak area.Data modeling showed that the tanks-in-series was more sensitive to wall effects, had good adjustment with only one tank for upward and horizontal flow and needed two tanks for downward flow which was attributed to the latter having higher dispersion. A black box empirical modeling described better the gravitational effect and allowed to identify a parameter sensitive to upward and downward flow as well as hinting to two inner streams within the horizontal flow. It also pointed to a wall dispersion contribution of twice that of the liquid-liquid dispersion.     

Spectral characterisation of new organic fluorescent dyes with an alkoxysilane moiety and their utilisation for the labelling of layered silicates

New fluorescence dyes with an alkoxysilane moiety were synthesised by the condensation of 3-(triethoxysilyl)-1-propanamine (3-aminopropyltriethoxysilane) with 4,10-benzothioxanthene-3,1′-dicarboxylic acid anhydride (BTXA) and N,N-dimethylaminonaphthalene-1,8-dicarboxylic acid anhydride (DMANA), which was accompanied by the formation of an imidic bridge. The compounds N-(3-(triethoxysilyl)propyl)-thioxantheno[2,1,9-dej]isoquinoline-1,3-dione (BTX-S) and 4-(N′, N′-dimethyl)-N-(triethoxysilyl)propyl-1,8-naphthalene dicarboxylic acid imide (DMAN-S) were characterised by steady-state and time-resolved fluorescence spectroscopy in chloroform and ethanol. Both conjugates (BTX-S and DMAN-S) exhibited absorption and emission bands in the same region as the un-substituted BTXA and DMANA. An important Stokes shift was observed for DMAN-S in ethanol. A high fluorescence quantum yield was observed for BTX-S in both solvents and for DMAN-S in chloroform. In addition, the newly developed fluorescent silane dyes were covalently attached to the microscopic particles of layered silicates and on the surface of SiO₂ wafers as a proof of concept for fluorescence particle (surface) visualisation. The surface wafer modification was precisely characterised by X-ray photoelectron spectroscopy (XPS). Successful covalent linkage onto the particles of layered silicates was proved by confocal laser scanning microscopy technique.     

Tetraaryl-methane analogues in group 14—V. Distortion of tetrahedral geometryin terms of through-space π–π and π–σ interactions andNMR sagging in terms of π–σcharge transfer

44 members of thecompound series Ph_4−nMR_n (M=Si, Ge, Sn, Pb; R=o-, m-, p-Tol; n=0–4) were synthesized (15 newcompounds). The crystal structures of Ph₃Sn (o-Tol) and PhSn (o-Tol)₃ were determined and compared to 16 known structures. Subject to the distanced (M–C), an interplay between through-space π–π repulsion and π–σ attraction leads to either elongated or compressed tetrahedral geometry. ²⁹ Si-, ¹¹⁹ Sn- and ²⁰⁷ Pb-NMR chemical shifts were determined in solution and in the solid state. ⁷³ Ge chemical shifts were measured only in solution. Anupfield or downfield sagging of the chemical shifts along each series is rationalized in terms of a π–σcharge transfer which is constrained by torsion of the aromatic groups.     

Optical spectra and localization of excitons in inhomogeneous helical cylindrical aggregates

We study the linear optical properties of helical cylindrical molecular aggregates accounting for the effects of static diagonal disorder. Absorption, linear dichroism, and circular dichroism spectra are presented, calculated using brute force numerical simulations and a modified version of the coherent potential approximation that accounts for finite size effects by using the appropriate open boundary conditions. Excellent agreement between both approaches is found. It is also shown that the inclusion of disorder results in a better agreement between calculated and measured spectra for the chlorosomes of green bacteria as compared to our previous report, where we restricted ourselves to homogeneous cylinders [Didraga, Klugkist, and Knoester, J. Phys. Chem. B 106, 11474 (2002)]. For the excitons that govern the optical response, we also investigate the disorder-induced localization properties. By analyzing an autocorrelation function of the exciton wave function, we find a strongly anisotropic localization behavior, closely following the properties of chiral wave functions which previously have been found for homogenoeus helical cylinders [Didraga and Knoester, J. Chem. Phys. 121, 946 (2004)]. It is shown that the circular dichroism spectrum may still show a strong dependence on the cylinder length, even when the exciton wave function is localized in a region small compared to the cylinder's size.